1. Field of Invention
The present invention pertains to the field of digital to analog conversion circuits. More particularly, this invention relates to a digital to analog converter with a dynamic current mirror structure.
2. Art Background
Electronic systems that drive electronic transmission lines may employ wave shaping techniques. Such a wave shaping technique usually includes the synthesis of sinusoidal waveform pulses from stored digital waveform data samples. Such an electronic system typically includes an digital to analog conversion circuit that converts sequences of digital waveform data samples to an analog signal. Typically, such digital waveform data samples provide input codes for the digital to analog conversion circuit.
Some prior electronic systems implement a differential digital to analog conversion circuit. Such differential digital to analog conversion circuits typically include a set of current sources which are coupled to corresponding switching transistors. Typically, the switching transistors are controlled by the input codes to the digital to analog converter. Such a combination of switched current sources yields a sum of electrical currents at output nodes that directly drive a pair of differential output resistors.
Unfortunately, such differential digital to analog converter circuits usually suffer from high power consumption. Typically, the output nodes coupled to the output resistors are biased to a preselected voltage level Such a preselected bias level is usually selected for maximum dynamic range in the analog output signal. Such biasing usually causes electrical current flow through the output resistors even while the output waveform is inactive. Such quiescent levels of output current unnecessarily consumes power during idle transmission periods.
In addition, such differential digital to analog conversion circuits typically generate high frequency noise through the output resistors. As a consequence, such differential digital analog converters usually include a low pass filter circuit to reduce such high frequency noise. Unfortunately, the extra components of such a low pass filter usually increase the size and the overall cost of such circuits.
Moreover, such differential digital analog converter circuits are typically implemented with relatively large transistors which are capable of delivering sufficient levels of current to the output nodes. Unfortunately, such relatively large transistors increases the integrated circuit die space required to implement the digital analog conversion circuitry which increases overall system costs.
Other digital analog conversion circuits include an operational amplifier configured as a voltage controlled voltage source. Typically, such an operational amplifier samples a low power input signal and generates a continuous signal at the required power to drive the load resistors at the output node. Such operational amplifier designs usually provide a high gain design along with feedback circuitry to provide overall stability In addition, such operational amplifiers typically require a high gain-bandwidth products to achieve stability Unfortunately, such a high gain closed loop circuit is inherently unstable and can cause undesirable oscillation in the analog output signal.